A touch panel or screen is one of the major interfaces between human and machine, and as a location recognition device, can ingeniously combine input and display interfaces, and therefore has the advantages of saving device space and user-friendly operation. Nowadays it has been generally applied to a wide variety of consuming or industrial electronic products. For example, PDAs (Personal Digital Assistant), palm-sized PCs (Personal Computers), tablet computers, mobile phones, handwriting input devices for a smart phone, IAs (Information Appliances), ATMs (Automated Teller Machines) and POS (Points-of-Sale), etc., which can generally be seen in various occasions of business and industry applications.
A touch panel can recognize more precisely the touch point of an external object with electrical conductivity by a device detecting electric capacity and thus sensing the change of electric field to recognize the location of the touch point. Please refer to FIG. 1, which is a diagrammatic sketch of a conventional projected-capacitive touch panel 100. The touch panel 100 includes a plurality of first electrode (i.e. driving electrode) stripes 120 and a plurality of second electrode (i.e. sensing electrode) stripes 130 both on an active area. The driving electrode stripes 120 and the sensing electrode stripes 130 are overlapped but insulated from each other. The driving electrode stripes 120 and the sensing electrode stripes 130 are electrically connected to a control unit 110. The control unit 110 can transmit detected touch event information through other interfaces to other circuit or module, such as a CPU of a computer system.
When the active area is scanned, the control unit 110 makes the driving electrode stripes 120 issue driving signals in turn, which then make the sensing electrode stripes 130 detect. When one of the driving electrode stripes 120 is driven and the electrical changes of the sensing electrode stripes 130 is detected, the control unit 110 can determine that a touch event occurs within or near the overlapped area of the driving electrode stripes 120 and the sensing electrode stripes 130.
As a result, to scan the overlapped areas of the driving electrode strips 120 and the sensing electrode stripes 130, the driving electrode strips 120 must be driven in turn and the sensing electrode stripes 130 are detected in sequence. Assuming the time of detecting the electrical change on the sensing electrode stripes 130 simultaneously is t and the number of the driving electrode strips is M, then total time for scanning the active area is M*t. However, the control unit 110 actively and repeatedly drives the driving electrode stripes 120 in turn under the operating status after the conventional projected-capacitive touch panel 100 is turned on. Even if no external object with electrical conductivity touches the active area, the control unit 110 still repeatedly drives the driving electrode stripes 120 in turn. Thus, the control unit 110 repeatedly reports the CPU more and more times in per unit time, while most of the detected and reported signals are invalid, causing unnecessary power consumption on the touch panel 100.
Summarily, since users demand for higher and higher functionality for all kinds of electronic devices, the electronic devices need to drive various systems, causing a lot of loss of power. Moreover, with the users' demand for the longer standby time of electronic devices, a touch panel and a controlling method thereof capable of effectively saving consumed power are needed on the market.